ENVIRONMENTAL DRIVERS AND BIOGEOCHEMICAL CONSEQUENCES OF BENTHIC EXTINCTIONS IN THE EARLY TRIASSIC

The end-Permian mass extinction (EPME) was devastating for shallow marine benthic ecosystems. In particular, bioturbators – animals that burrow into and mix seafloor sediments – were profoundly impacted by the EPME. The global trace fossil record indicates that in most regions on Earth, there was a significant reduction in mixing depth and intensity during the Early Triassic. This has been previously hypothesized to have resulted in major disruptions in global biogeochemical cycles due to the loss of the sedimentary mixed layer, potentially contributing to delayed ecosystem recovery throughout the Early Triassic. However, recent work has demonstrated that strong, deep-tiered bioturbation persisted in some regions, and these bioturbators may have maintained local nutrient cycling in spite of climate-related stress driven by the EPME. Here, we investigate the environmental conditions that may have allowed effective bioturbators to persist in the Early Triassic and the local benthic biogeochemical consequences of their survival and extinction. We use the Earth system model cGENIE to reconstruct paleoenvironmental conditions in the Early Triassic regions that host robust trace fossil records today. We investigate local drivers of the extinction or survival of bioturbators by linking the trace fossil record to key physiological variables (oxygen, temperature, and organic matter) from these modeled reconstructions. We then combine data from the trace fossil record and outputs from our paleoenvironmental reconstructions with a sedimentary biogeochemical model to simulate how regional extinction patterns in the Early Triassic would have impacted local key nutrient cycles, including carbon and phosphorus. These results offer new insights into how the spatial variability of extinction events may be explained by physiological variables, as well as how bioturbators have acted as important ecosystem engineers during intervals of climate change throughout Earth history.